Process for producing carbon fibres

ABSTRACT

A PROCESS FOR THE PRODUCTION OF CARBON FIBRES FROM COAL TAR PITCH OR FROM OTHER STRONGLY AROMATIC DISTILLATION RESIDUES SUBJECTED TO HEAT TREATMENT AT A MODERATE TEMPERATURE WHEREIN A HYDROCARBON POLYMER IS ADDED TO THE STARTING MATERIAL BEFORE OR DURING SAID HEAT TREATMENT WHICH IS FOLLOWED BY SPINNING, OXIDIZING, AND CARBONIZING. POLYETHYLENE, POLYPROPYLENE, POLYSTYRENE, POLYBICYCLO (2,2,1)HEPTENE-2, AND RUBBER ARE PREFERRED POLYMERS.

United States Patent 3,784,679 PROCESS FOR PRODUCING CARBON FIBRESPierre Chiche, Verneuil-en-Halatte, France, assignors to Charbonnages deFrance, Paris, France No Drawing. Filed Apr. 27, 1971, Ser. No. 137,976Claims priority, applic7altigri7ll rance, May 19, 1970,

Int. Cl. C01b 31/07 Us. or. 423-447 11 Claims ABSTRACT OF THE DISCLOSUREThe present invention concerns a process for producing carbon fibresfrom coal-tar pitch or from other strongly aromatic distillationresidues.

Carbon fibres have already been obtained from coal-tar pitch bysubjecting the said pitch to 'a heat treatment at a moderate temperatureand possibly to other treatments or conditioning, and thereafterspinning the pitch so treated at a temperature of the order of 300 C.The fibres so obtained were subjected to oxidation to render theminfusible, and then carbonized in air. However, these processes resultin fibres of a much inferior quality, and mechanical properties to thoseproduced from textile (e.g. rayon or poly-acrylonitrile) filaments butthe latter are generally expensive to produce.

iAll object of the present invention is to provide a process whichallows an improvement in the quality of the fibres obtained fromcoal-tar pitch or from another strongly aromatic substance like coal-tarpitch.

Another object of the present invention is to provide improved fibresobtained from this process.

According to the process of this invention, there is provided a processfor the production of carbon fibres from a strongly aromaticdistillation residue comprising subjecting the said residue to a heattreatment at a moderate temperature, a hydrocarbon polymer being addedto the said residue, before or during the heat treatment, the

product of the heat treatment being thereafter spun into fibres whichare then oxidized and carbonized.

Among the preferred polymers embodied in this invention and giving goodresults, one can mention natural or synthetic polymers such aspolyethylene, polypropylene, polystyrene, polybicyclo[2,2,1]-heptene-2,rubbers, etc.

According to a preferred embodiment, the filtered strongly aromaticpitch is heated, before spinning under conditions of temperature, andfor 'a length of time, as well as with agitation, such that the obtainedmaterial contains no or only a little anisotropic material; in otherwords, the heat treatment is stopped at the latest at the beginning ofthe onset of the anisotropic phase. The presence of anisotripic materialcan easily be evidenced by examination with a polarized light opticalmicroscope (M. Ihnatowicz, P. Chiche, J. Deduit; S. Pregermain and R.Tournant, Carbon, 4, 41 (1966)). This heat treatment can be achieved ina reactor provided with an agitation or stirring system and means forscavenging gases.

One may alternatively heat the mixture to a distinctly lower temperaturebut the reduced de-volatilization or the volatilizing-ofi' of thematerial so obtained renders the oxidation treatments, necessary formaking the filaments infusible before carbonization, more difficult.

'ice

The scope of this invention includes carbon fibres made by the processas set forth above.

The following examples will serve better to throw into relief theadvantages of this invention.

EXAMPLE 1 A high temperature coal-tar pitch with the followingcharacteristics was utilized:

Kraemer-Sarnow point C Density g /cm. 1.32 Index of volatile materials(according to the standard ATIC-02-60) percent 64.3 Elemental analysisin percentage by weight:

Carbon 93.02 Hydrogen 4.45 Oxygen 1.5 Nitrogen 0.7 Sulphur 0.3

This pitch was previously filtered 'at C. over a bronze filter with meanpore size of 2,1 in order to separate out the solid and pseudo-solidparticles that the pitch contains naturally.

After adding 10% by weight of melt-index 4, high densiy polyethylene,this mixture was heated to 420 C. under constant agitation at a heatingrate of 3 C./minute; the generated volatile materials were entrained ina stream of nitrogen flowing at 3 l./min.

The resulting product was spun at 204 C. at a drawing speed of 450m./minnte.

The whole of this was then placed in a furnace and subjected to thefollowing operational conditions:

Hours From room temperature to 250 C. in the presence of air at aheating rate of 05 C./minute 7.5 From 250 C. to 700 C. in the presenceof nitrogen and in the absence of oxygen, at a heating rate of 05C./minute 15 From 700 C. to 1000 C., at a heating rate of 2 C./minute2.5

Total 25 The furnace was then allowed to cool naturally. The mechanicalproperties of the resulting carbon fibres were measured with the aid ofan Instron press, under the following conditions:

Length of test-tube mm 50 Pulling speed cm./minute 0.05

'In this way a mean breaking strength of 55 kg./mm. was measured as wellas a mean Youngs modulus of 4200 kg./mm. and a mean diameter of 30,11.

These values represent the averages taken from 7 readings effected ondifferent filaments. The total yield of the operations comprising thefiltering, de-volatilization, spinning, oxidation and carbonization was65%.

EXAMPLE 2 The total yield of the operations as described in Ex-,

ample 1 was 66%.

3 EXAMPLE 3 The operating conditions were identical with those inExample 1, except that the polyethylene was replaced by a polystyrene.

The thus prepared carbon fibres were measured to have a mean breakingstrength of 60 kg./mm. and a Youngs modulus of 4600 l g./mm. for adiameter of 30 The total yield of the operations as described in Example1 was 64% EXAMPLE 4 (NOT ACCORDING TO THIS lNVENTION) The operatingconditions were identical with those in Example 1, but here the pitchdid not receive any additive.

The carbon fibres prepared in this way were measured to have 'a meanbreaking strength of 24 kg./mm. and a Youngs modulus of 3300 kg./mm. fora diameter of 30 1.

The total yield of the operations as described in Example 1 was 61% Theadvantages of the invention are thus apparent by comparing theseproperties with those of the fibres according to the invention describedin Examples 1 to 3.

I claim:

1. In a process for the production of carbon fibres from a stronglyaromatic distillation residue pitch comprising subjecting said pitch toa heat treatment at a temperature on the order of about 420 C., theproduct of the heat treatment being thereafter spun into fibres whichare then oxidized and carbonized, the improvement comprising adding ahydrocarbon polymer in an amount suflicient to improve the mechanicalproperties of the carbonized fibres to said pitch no later than duringsaid heat treatment, said hydrocarbon polymer being selected from thegroup consisting of polyethylene, polypropylene, polystyrene,polybicycle[2,2,l]-heptene-2 and rubber.

2. A process as claimed in claim 1 wherein the said polymer is addedbefore the heat treatment.

. 3. A process as claimed in claim 1 wherein the said polymer is apolyethylene.

4. A process as claimed in claim 1 wherein the said polymer is apolypropylene.

5. A process as claimed in claim 1 wherein the said polymer is apolystyrene.

6. A process as claimed in claim 1 wherein the said polymer is apolybicyclo[2,2,1]-heptene-2.

7. A process as claimed in claim 1 wherein the said polymer is a naturalor synthetic rubber.

8. A process as claimed in claim 1 wherein the heat treatment is stoppedbefore the onset of the anisotropic phase in the pitch.

9. A process as claimed in claim 1 wherein the heat treatment is stoppedat the beginning of the onset of the anisotropic phase in the pitch.

10. A process as claimed in claim 1 wherein the said pitch is coal-tarpitch.

11. A process in accordance with claim 1 wherein said hydrocarbonpolymer is used in an amount on the order of about 10% by weight.

References Cited UNITED STATES PATENTS 3,629,379 12/1971 Otani 423447 X3,639,953 2/1972 Kimura et a1. 423447 3,607,672 9/1971 Schmitd 4234473,392,216 7/-l968 Otani 26429 3,595,946 7/1971 000 et al 26429 3,107,15310/ 1963 Boquist 423448 OTHER REFERENCES MacKay et al.: Modern Plastics,vol. 45, No. 2, 1968, pp. 147-150.

EDWARD J. MEROS, Primary Examiner U.S. Cl. X.R. 26429

